Thermally conductive paper containing dendritic metal particles



May 12, 1964 R. N. STENERSON 3,132,989 THERMALLY CONDUCTIVE PAPER CONTAINING DENDRITIC METAL PARTICLES Filed F'eb. 27, 1961 INVENTOR.

RANDOLPH N. STENERSON J7 Wm ATTORNEY.

3,132,989 Patented May 12, 11964 THERMALLY CONDUCTIVE PAPER CONTAINING DENDRITIC METAL PARTICLES Randolph N. Stenerson, De Witt, N.Y., assignor to Carrier Corporation, Syracuse, N.Y., a corporation of Delaware Filed Feb. 27, 1961, Ser. No. 91,735

14 Claims. (ill. 162 181) This invention relates generally to the art of paper making, and more particularly to the manufacture of paper metal-like in character. Still more particularly, this invention relates to an improved material formed from a fibrous body having dendritic metallic particles distributed therethrough. Further, this invention relates to the making of an improved paper having metal-like qualities, the paper being comprised of cellulose fibers intermeshed and entwined with dendritic copper particles.

Heretofore, the manufacture of metallic paper, also known as metaliz'ed paper, has not been altogether successful. Often a metallic compound was introduced into the paper stock and the desired metal was precipitated out from the compound to blend with the cellulose fibers. The paper so formed did not have a satisfactory distribution -of metal and in the manufacture of the paper the precipitated metal particles sometimes adhered to the components of the paper making apparatus. Too, only a limited amount of the paper would be comprised of metal. To increase the quantity of metal within the paper sheet to enhance the thermal and electrical properties thereof, metallic particles were added to the wood pulp.

- The commercially available powdered metal consists of particles having a generally chunky or spheroidal configuration. Such powdered metal tended to separate from the cellulose fibers rather than to adhere to these fibers. The distribution of these metal particles was unsatisfac tory for the desired purposes. v

. An object of this invention is to overcome the disadvantages and deficiencies inherent in the prior attempts to successfully blend metal particles and paper pulp.

; Another object of this invention is to provide a novel sheet material formed from a fibrous mass blended with dendritic metallic particles.

It is another object of this invention to provide a novel process for forming metallic paper.

Still another object of this invention is to provide a novel sheet material formed from a fibrous body having dendritic metallic powder distributed therein.

A further object of this invention is to provide a novel conductive specialty paper formed from cellulose fibers and dendritic metallic powder having desirable electrical and thermal properties.

7 A still further object of this invention is to provide a method of forming a novel conductive paper.

. Yet another object of this invention is to. provide novel heat exchanger "fin stock formed from fibers interlaced with dendritic metallic powder to form a substantially continuous path for the flow of heat through the fin stock.

This invention relates to the manufacture of sheet material comprising a fibrous body and dendritic metallic powder distributed throughout the fibrous body. The sheet material may be made on commercial paper making machines as for example a Fourdrinier machine to yield a material predominately metallic in character, which material possesses desirableithermal and electrical properties.

This invention further relates to a method of forming a conductive paper comprised of cellulose fibers and den dn'tic copper powder interlaced with the cellulose fibers.

These and other objects of this invention will become apparent when the following description is read in conjunction with the accompanying drawing wherein:

FIGURE 1 is a perspective view of a sheet of material embodying the present invention;

FIGURE 2 is a perspective view of a heat exchanger having plate fins made from the metallic paper of the present invention.

By using dendritic powdered metal, it is possible to produce paper having compositions and properties not heretofore obtainable by the known methods of making paper. For example, the spherical copper particles heretofore used in the manufacture of copperized paper had a" tendency to separate from the fibrous stock and only a small amount of copper was retained in the resultant sheet.

I discovered that dendritic metal particles or powder such as may be produced by. electrolytic deposition of the metal may be effectively blended with a fibrous body to form a product having useful thermal and electrical properties. The dendritic particles are characterized. by a pine tree configuration. During the process of electrodeposition of a pure metal, a primary axis is formed and to this are added secondary and tertiary branches giving rise to a skeleton resembling a pine tree. As growth or particle formation proceeds, these axes become longer and thicker. These dendritic particles cling and commingle with the fibers in the paper. The resultant product could be made by conventional paper making. In one form of the invention wood pulp was blended with dendritic copper powder to form a metallic sheet 2 (FIG- URE 1) having adequate mechanical strength and desirable thermal conductivity for use as heat exchanger fin stock.

The following example is given to illustrate the application of the present invention:

Example 1.-To a mixture of hard wood bleached kraft pulp was added a slurry containing dendritic copper powder. After thoroughly blending the ingredients for ten minutes, paper sheets were formed. The formed sheets Were placed under a pressure of 3,000 psi to reduce the sheet to the desired thickness and to mechanically blend the copper within the wood fiber matrix. The copper powder within the sheet was equal to three times the dry weight of the wood pulp. The paper so formed gave a metallic copper appearance and had acceptable thermal conductivity and workability for use'as heat exchanger fin stock.

Example 2.A paper sheet was formed as in Example 1, wherein the weight of the dendritic copper powder was twice the weight of the wood pulp. The paper sheet formed had a metallic copper appearance and also possessed a desirable thermal conductivity.

Example 3.--A paper sheet was formed as in Example 1, wherein the weight of the copper powder was sixteen times the weight of the dry hard wood bleached kraftpulp. This sheet had suitable thermal properties for use as heat exchanger fin stock.

The paper sheets may be further compressed by suitable hydraulic or mechanical means to further increase the intimacy of contact of the copper particles withinthe paper sheet to increase the electrical and thermal properties of the paper sheet.

Other dendritic metal powders, as, for example, silver, zinc, chromium, cadmium, nickel or iron powder might be used in place of dendritic copper powder.

The proportion of dendritic metal powder to the wood pulp may be varied to produce different properties of the metallic paper. To produce a paper sheet having adequate thermal conductivity for use as heat exchanger fin 3 quantity of copper may be varied from approximately 1% to 90% to achieve the desired eifect.

The mechanical properties of the metallic paper manufactured according to the present invention may be improved by laminating the paper with melamine resin or other resins or by impregnating the sheets with suitable resins. It will be apparent to those skilled in the art that other fibers maybe substituted for the cellulose fibers. Glass, rubber or synthetic fibers with suitable bonding resins can be substituted for the cellulose fibers to vary the water resistance, heat resistance and other properties of the material.

Referring now to FIGURE 2, there is shown a heat exchanger 3 having fin sheets 4'there0n. The fin sheets are made from metallic paper formed in accord with the teachings of the present invention. Suitable openings are provided in the fin sheet to accommodate the tubes 5 of the heat exchanger. The tubes 5 are in intimate contact With the fin sheets to extend the effective heat transfer surface of the tubes. The ends of the tubes are connected to suitable headers 6 and 7. An inlet 8 is secured to header 6 and an outlet 9 is secured to header 7. The heat exchanger may be used as an evaporator or condenser in a conventional refrigeration system. It is contemplated that the novel fin stock might be used with other heat exchangers, as for example, a heat exchanger comprised of a serpentine coil.

It has been observed that the metallic paper formed in accord with the teachings of the present invention acted like a blotter when brought into contact with water. This porosity or blotting efiect could be used advantageously in the formation of a unique heat exchanger fin stock. For

metal particles comprise at least two-thirds of the weight of the fin stock.

example, the fin sheets of a condenser might extend into the condensate. The fin stock formed according to the present invention would absorb the condensate. The air passing over the condenser would evaporate the water to enhance the heat transfer capabilities of the condenser and to etfect a greater cooling of the refrigerant within the condenser tubes than was heretofore possible.

Another application of this invention is resistance paper. By connecting the paper sheet formed of fibrous material having dendritic metallic particles interspersed therethrough to a suitable source of electrical current, the resistance of the sheet would cause the sheet to warm. Such resistance paper might be used like radiant heat panels to provide auxiliary heat with which to warm an enclosed environment.

An important advantage in the manufacture of the novel metallic paper is that it can be commercially made on standard paper making equipment. The material formed from the fibrous body, intermeshed and interlaced with dendritic metallic powder, has desirable'thermal and electrical properties. The cost of heat exchanger fin stock previously made from copper and aluminum may be materially reduced by using heat exchanger fin stock formed from the metallic paper of the instant invention.

Further advantages and modifications of this invention will be obvious to those persons skilled in the art and I desire that this invention be limited only by the scope of the appended claims.

I claim: I

1. A material comprised of a fibrous mass having metallic particles of dendritic form interlaced and interspersed throughout the mass.

2. A material as in claim 1 wherein said fibrous mass is comprised of cellulosic fibers.

7. 7 Heat exchanger fin stock as in claim 6 wherein said metal particles are copper.

8. Heat exchanger fin stock as in claim 6 wherein said fibrous body is comprised substantially of natural cellulosic fibers.

9. Heat exchanger fin stock as in claim 6 wherein said fibrous body is comprised at least in part of synthetic fibers.

10. As a new article of manufacture, a thermal conductive material comprising a dehydrated mixture of cellulose fibers having metal particles of dendritic form interspersed and intermingled throughout so as to adhere to the cellulose fibers and to one another, said material suitably.

formed to provide a physical structure of a predetermined configuration, said metal particlesproviding a. substantially continuous path within the material for the flow of heat.

11. A thermal conductive specialty material comprising a fibrous mass'containing not less than two-thirds by weight of dendritic metallic powder, the metallic powder being freely distributed in the interstices of and clinging to the surface of the fibrous mass so as to form a substantially continuous path for theflow of heat through said material 12. A thermal conductive specialty paper comprising cellulose fibers and dendritic copper powder, the copper powder being distributed throughout the fibers and being commingled and interlaced with the fibers to form a substantially continuous path for the flow of heat through said paper.

13. A process for making conductive cellulosic paper which comprises adding to paper stock dendritic metallic particles in a quantity at least twice the dry weight of the wood pulp of the paper stock, blending the mixture of paper stock and dendritic metallic particles to distribute the metallic particles throughout the paper stock and thereafter forming a paper sheet from said stock.

14. A process as in claim 13 including the step of press- 7 ing the paper sheet.

References Cited in the file of this patent UNITED STATES PATENTS vol. 42, No. 5, pp. 96-98, November 1955. 

5. AS A NEW ARTICLE OF MANUFACTURE, HEAT EXCHANGER FIN STOCK FORMED FROM A FIBROUS BODY HAVING AS AT LEAST ONE CONSTITUTENT THEREOF DENDRITIC METAL PARTICLES INTRESPRSED AND INTERLACED WITH THE FIBROUS BODY SO AS TO FORM A SUBSTANTIALLY CONTINUOUS PATH FOR THE FLOW OF HEAT. 